1. Technical Field
The present invention relates to a method of producing a metal structure by photoreduction of metal ion. More specifically, the present invention relates to a method of manufacturing a metal structure, whereby processing resolution thereof is improved by suppressing growth of metal crystal constituting the metal structure.
2. Background Art
In recent years, fine processing technologies using light such as optical lithography technology and optical disk manufacturing technology are widely utilized, and such technologies have been studied in a variety of fields.
For example, the fine processing technology using light, which is most widely applied at present, is the above-mentioned optical lithography technology. The optical lithography technology is a backbone technology for manufacturing a variety of electronic devices such as semiconductor chips. The technology relates to a massive copying technology using a photo-transferring technology in principle, in which a metal in a specified region is dissolved, separated out, or removed finally in a chemical manner, thereby a desired metal pattern is formed as a metal structure. Therefore, this method may be used only for two-dimensional processing, and it is impossible to use the method to freely form a metal structure having a three-dimensional structure.
On the other hand, a technique for forming a metal pattern by irradiating directly a laser beam on a specified material is known as a technology for forming a desired metal pattern as a metal structure other than the above-mentioned optical lithography technology. More specifically, there are a technique involving irradiating a focused laser beam onto a medium having metal nanoparticles dispersed therein, to thereby melt and bind the metal nanoparticles at the focal point of the laser beam, thereby a metal pattern is formed as a metal structure; and a technique involving irradiating focused light onto metal ion, thereby the metal ion is photoreduced and a metal body is separated out, thereby a metal pattern is formed as a metal structure.
Here, in the above-mentioned technique involving separating out the metal body by photoreducing the metal ion, an arbitrary metal pattern can be formed as a metal structure in response to the track of scanned focused laser beam by scanning the focused laser beam which irradiates the material ion. Accordingly, a metal structure having a three-dimensional structure can be freely formed, and its applicable range is extremely wide, thereby studies and developments have been made upon the technique in a variety of fields in recent years.
A method of improving the processing resolution of the metal structure in the technique involving photoreducing the metal ion to separate out the metal body is also known.
In general, an absorption rate of light increases when metal structure is separated out, and hence there are many cases where the reaction proceeds explosively just at the moment when an increased amount of the metal structure exceeds a certain threshold value. There is a problem that, when such a phenomenon occurs, the photoreduction of the metal ions existing in the vicinity of the focal point proceeds at the same time, thereby the processing resolution of the metal structure degrades. In the method disclosed in JP2006-316311A, a specified pigment is added to a material, thereby an absorption spectrum and an absorption cross section of a non-processed material are maintained at constant, and the processing resolution is prevented from degradation by propagating energy of the laser beam to an area other than the focal point of the laser beam, besides photoreduction efficiency at the focal point of the laser beam is improved.
This method could improve the processing resolution to a micrometer order, but a higher-precision nanometer-order processing resolution was yet required.